APOPTOSIS OF FAS(HIGH) CD4(-CELLS BY BORRELIA-REACTIVE FAS-LIGAND(HIGH) GAMMA-DELTA T-CELLS IN LYME ARTHRITIS() SYNOVIAL T)

The function of the minor subset of T lymphocytes bearing the gamma de lta T cell antigen receptor is uncertain. Although some gamma delta T cells react to microbial products, responsiveness has only rarely been demonstrated toward a bacterial antigen from a naturally occurring hu man infection. Synovial fluid lymphocytes from patients with Lyme arth ritis contain a large proportion of gamma delta cells that proliferate in response to the causative spirochete, Borrelia burgdorferi. Furthe rmore, synovial gamma delta T cell clones express elevated and sustain ed levels of the Ligand for Fas (APO-1, CD95) compared to alpha beta T cells, and induce apoptosis of Fas(high) CD4(+) synovial lymphocytes. The findings suggest that gamma delta T cells contribute to defense i n human infections, as well as manifest an immunoregulatory function a t inflammatory sites by a Fas-dependent process.